=== Updated by MModell
I'm hijacking this task to track our plan for keeping arc in sync with phab updates.
> Which backward and forward compatibility guaranties is given for arcanist and/or the APIs it uses?
> If there were none, that would mean that each time a Phabricator update is done everyone needs to upgrade arcanist to a specific version and they would need a different arcanist version for every Phabricator installation. Some upstream documentation regarding their compatibility guaranties would help us not running into this problem unexpectedly.
The short answer is, there are no guarantees.
We need to deal with this by providing a supported version of Arcanist and a way for users to easily update. It's pretty straightforward - users need to install symlink to the arc executable checked out from git, and then they can run git pull to update.